Many drugs in use today are “small molecule drugs.” These drugs exist as simple chemical structures that are synthetically derived. The active ingredient generally exists as a homogenous product. These small molecule drugs and preparations thereof, can be chemically characterized using a variety of analytical tools and are generally readily manufactured through comparatively simple chemical synthesis.
A typical glycoprotein product differs substantially in terms of complexity from a typical small molecule drug. In particular, the sugar structures attached to the amino acid backbone of a glycoprotein can vary structurally in many ways including, sequence, branching, sugar content, and heterogeneity. Thus, glycoprotein products can be complex heterogeneous mixtures of many structurally diverse molecules which themselves have complex glycan structures. N-linked glycans are an important class of branched sugars found in glycoproteins which have a conserved core structure with variations in branching and substitutions of the sugar residues. Glycosylation adds not only to the molecules structural complexity but affects or conditions many of a glycoprotein's biological and clinical attributes.
To date, the creation of glycoprotein drugs having defined properties, whether an attempt to produce a generic version of an existing drug or to produce a second generation or other glycoprotein having improved or desirable properties has been challenging due to the difficulty in synthesizing and characterizing these complex chemical structures and mixtures that contain them.
The situation with regard to the production of generic products is indicative of the problems faced in making glycoprotein drugs having defined properties. While abbreviated regulatory procedures have been implemented for generic versions of small molecule drug products, many in the biotechnology and pharmaceutical industry have taken the view that the complexity of glycoprotein drug products makes them unsuitable for similar approaches.
There is therefore a need in the art for methods for characterizing glycoproteins. In particular, there is a need for analytical methods that are capable of characterizing complex mixtures of glycans, e.g., mixtures obtained by cleaving a plurality of N-glycans from a glycoprotein preparation.